Capacitive touch screens have become standard input devices for mobile electronic devices. Controllers for driving capacitive touch screens generally have a frequency hopping function. Active styluses have gradually appeared on the market in recent two years. For example, HTC, Ntrig, and Goodix all have launched their active stylus products. An active stylus needs to be used with a capacitive touch screen. FIG. 1 is a schematic structural view of a touch screen. As shown in FIG. 1, the main components are two sheets of glass. The upper glass is a Coverlens that serves as a touch surface and also has a protection function. The lower layer of glass is a sensor substrate, with driving electrodes and sensing electrodes distributed on an upper surface, and a shielding layer (optional) distributed on a lower surface. The two sheets of glass are usually attached together by means of an ultraviolet (UV) adhesive or an optical clear adhesive (OCA). A flexible printed circuit (FPC) with a capacitive touch screen control integrated circuit (IC) and a peripheral circuit is bonded to the driving and sensing electrodes.
FIG. 2 is a schematic view of Driving & Sensor electrodes that form a vertical intersection matrix structure. As shown in FIG. 2, a capacitive touch screen subsystem needs to detect a touch of a hand and a touch of an active stylus. The two types of detection correspond to different modes. When a finger touch operation is detected, as shown in FIG. 3, the driving electrodes generate a driving signal, and the sensing electrodes receive the driving signal. When the active stylus is detected, as shown in FIG. 4, the driving electrodes are connected to a sensing circuit unit through a multiplexing circuit, the sensing electrodes are also connected to the sensing circuit unit through the multiplexing circuit, and the driving electrodes and the sensing electrodes occupy the sensing circuit unit in different time periods.
An existing system composed of an active stylus and a capacitive screen employs only one-way communication from the active stylus to the capacitive touch screen, and cannot implement communication from the capacitive touch screen to the active stylus.
Such communication mode causes various problems to the application of the active stylus. For example, interference of different frequencies, typically liquid crystal display (LCD) interference, exists on different mobile products. A solution in the prior art is that for a specific customer project, an active stylus pre-appoints a frequency f without interference as an operating frequency of the stylus. Taking two projects as an example, it is possible that the stylus of project 1 needs to operate at frequency f1, while the stylus of project 2 needs to operate at frequency f2. In this way, stylus produced by even one manufacturer cannot be used universally, bringing a lot of inconvenience to the producer and users. An existing practice is that a stylus may generate different frequencies according to a user's selection, for example, selection made by the user through a key. For example, the operating frequency is switched once by pressing one key until the touch screen normally responds to the operation of the active stylus. Such practice alleviates the problem to a certain degree but still requires user intervention.